cases 1 - 3 give parametrizations for 2p2h part of structure function W1
in terms of Q^2, no distinction for neutrinos and antineutrinos
Cases 1 and 2 are those in: Lalakulich Gallmeister Mosel PRC86(2012)014614
Case 3 gives a reasonable description of MiniBooNE dd neutrino data
cases 4 - 5 give parametrization for MEC part of W1 from Christy and Bosted
In this case also W3 is related to W1 (acc. Martini and Ericsson)
Case 4 describes double-differential data from MiniBooNE for neutrino
and antineutrino scattering. It also describes the dd inclusive Xsection for
neutrinos from T2K.